The invention relates to weighing devices in general, and more particularly to improvements in weighing devices (hereinafter called scales for short) which employ strain gauges. Still more particularly, the invention relates to improvements in scales (including bathroom scales) wherein a platform can be acted upon by a selected load (such as the weight of a person standing on the platform) to change its position relative to a base (either entirely or in part) whereby the extent of displacement is proportional to the magnitude of the load. The displacement is ascertained by the strain gauge wherein an electric resistor changes its resistance to the flow of electric current at a rate which is a function of the extent of displacement (e.g., deformation) of the platform with reference to the base. The change of resistance is used to furnish indications denoting the magnitude of the applied load.
In certain presently known scales of the above outlined character, the platform is in two-point contact with a carrier in the base, and the strain gauge is located midway between the two points of contact. The gauge has an ohmic resistance which constitutes a transducer by generating an electric signal which is proportional to the magnitude of applied load, and the signal is amplified and used to change the position of a pointer or hand with reference to a graduated scale serving to indicate the magnitude of the applied load. The transducer has a support which is made of paper, a plastic material or the like and carries a wire-like resistor. The support is bonded to the carrier which is mounted in the base and supports the platform. The means for bonding the support to the carrier is a two-component synthetic resin adhesive which is sensitive to moisture. Therefore, the strain gauge is furnished as a separate part which is confined in a waterproof envelope consisting of wax, rubber, plastic or the like. It is considered necessary to place the resistor of the strain gauge exactly midway between the points of contact of the carrier with the underside of the platform. The resistor of the strain gauge is relatively short, and even minor deviations of the position of such resistor from an optimum position will result in extensive distortion of the results of measurements.
It has been found that the just described types of strain gauges often fail to operate satisfactorily, either because they are overly sensitive to moisture or because they furnish misleading measurements due to inaccurate mounting of the resistor. Moreover, they cannot be mass-produced at a reasonable cost.